Fibrous material comprised of vermiculte coated fibers

ABSTRACT

A fibrous composite material of essentially two-dimensional form in the form of individual fibres, sheets or layers comprising combustible fibres and lamellae of a layer mineral of size below 50 microns, a method for the manufacture of the fibrous composite materials by applying lamellae of a layer mineral to the fibres preferably from suspension followed by removal of the liquid phase of the suspension, and use of the fibrous composite materials for the fire-protection of substrates.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a division of our earlier application Ser. No. 545,103 filedOct. 24, 1983, now U.S. Pat. No. 4,442,164 which, in turn, is acontinuation of earlier application Ser. No. 281,104 filed July 7, 1981,now abandoned.

This invention relates to fibrous materials and particularly to fibrouscomposite materials comprising fibres which have been coated with orembedded in an inorganic material to upgrade the fibres, and to theproduction and use of the fibrous composite materials.

Fibres and fibrous materials made from them are notoriously susceptibleto damage or destruction by fire. Fibres, whether natural or man-madefibres, comprising organic materials, for example wool, cotton, rayon,cellulose acetate, polyesters, polyamides and lignocellulosic fibres arecombustible and generally readily flammable.

It would clearly be advantageous, for example in the textile, furnishingand building industries, if fibres and particularly the less expensive,organic fibres, could be upgraded to improve their fire performance e.g.fire resistance and flame retardancy, and numerous treatments have beenproposed for achieving this desirable result by coating the fibres withor embedding them within a fire-resistant material or by incorporating afire-resistant material in the fibre structure. Hitherto, nosatisfactory solution to the problem has been achieved; in particular nosolution has been found which combines satisfactory fire performancewith acceptable expense whilst retaining the flexible nature of thefibres and materials made from them.

According to the present invention there is provided a fibrous compositematerial of essentially two-dimensional configuration comprisingcombustible fibres and lamellae of a layer mineral wherein the lamellaeare substantially all of size below 50 microns. Preferably the fibrouscomposite material comprises at least 15% by weight and preferably atleast 20% by weight of the fibres.

There is also provided a method for the manufacture of the fibrouscomposite material by applying the lamellae to fibres, preferably fromsuspension in an inert carrier liquid.

The method for the manufacture of the composite material is also amethod of upgrading the fire-performance of combustible fibres.

Vermiculite is the preferred layer mineral. By "vermiculite" we mean allmaterials known mineralogically and commercially as vermiculite,including the chlorite-vermiculites.

By the term "lamellae of a layer mineral" as used throughout thisspecification we mean tiny particles of the layer mineral obtained bychemically delaminating the layer mineral into particles or plateletshaving a high aspect ratio. Thus for example vermiculite lamellaeobtained by chemical delamination are tiny platelets obtained bychemical delamination of vermiculite and having a thickness of less than0.5 micron, usually less than 0.05 micron and preferably less than 0.005micron, and having an aspect ratio (i.e. length or breadth divided bythickness) of at least 10, preferably at least 100 and more preferablyat least 1000, for example 10,000. The lamellae obtained by chemicaldelamination of other layer minerals are of similar dimensions to thoseof vermiculite lamellae.

Whilst vermiculite is the preferred layer mineral, other layer mineralswhich may be used include montmorilonite, Kaolinite (and clayscomprising sepiolite Kaolinite, for example kaolins and ball clays) andother layer-silicate minerals which can be chemically deliminated toprovide lamellae or plate-like particles.

The fibrous composite materials of the invention may have a wide varietyof forms and the layer mineral lamellae may be present in the compositeas a coating on the individual fibres of the composite, as a layer inwhich the fibres are embedded or as a coating or facing layer on the orboth sides of a fibrous material such as a woven fabric or a felt, or asan inner layer between layers of the fibrous material. By way ofillustration only and without in any way restricting the scope of thepresent invention, the following product forms are included within theterm fibrous composite material:

3 A layer of fibres faced on one or both sides with a layer of lamellae.

4 Strands comprising multiple filaments, e.g. 100 to 1000 filaments,having lamellae coated onto the individual filaments and/or onto thestrands.

5 Rovings comprising multiple strands twisted, doubled or pliedtogether, having lamellae coated onto the filaments and/or the strandsand/or onto the rovings.

6 A layer of fibres bonded together by lamellae.

It will readily be appreciated that each of the above product formscomprising a layer of fibres may comprise a multi-layer structure offibres and that the fibre layers may comprise loose fibres or may be awoven, knitted, needlepunched, felted or otherwise unified structure.Furthermore, it is to be understood that in any of the product forms ofthe fibrous composite material the fibres may be continuous(filamentary) or discontinuous (staple), or agglomerates of fibres.

The amount by weight of lamellae applied to the mass of fibrous materialmay vary within wide limits depending for example upon the intendedfire/temperature duty of the composite, the desired flexibility of thecomposite, the required degree of structural integrity of the compositebefore and after it has been subjected to a fine and whether thelamellae are applied as a coating or a facing for the fibrous material.In general, increasing the loading of lamellae on the fibrous materialwill increase the fire-performance of the fibres and the thermalconditions which the composite will withstand. We have observed,however, that in general very thin layers of lamellae, for example lessthan 1 micron thickness, are all that is required to upgrade thefire-performance and the high-temperature performance of the fibres. Asa guide only, the loading of the layer mineral on the fibres of thecomposite will usually be from 0.05% to 100% by weight, typically from0.1% to 20% by weight, of the fibres. Amounts of the layer mineralgreater than these may be used and indeed the composite may comprise asmuch or even more layer mineral than fibres such that the composite ineffect becomes a fibre-reinforced layer of lamellae, for example wherehigh flexibility in the composite is unnecessary or undesirable; theamount of fibres in such a structure should be at least 15% by weightand may be, for example from 20% to 50% by weight of the composite.

The amount of lamellae applied to the fibres will affect the degree ofdamage suffered by the fibres when the composite material is exposed toa flame or, to temperatures above the softening point of the fibres.Fibres coated thinly with the layer mineral may be charred or evenburned by a flame high temperature whilst increasing the coatingthickness increases the resistance of the fibres to damage by the flame.In most practical applications of the invention the fibres of thecomposite material are likely to be damaged or even completely burned bya flame or high temperatures, but in spite of this the fire-performanceof the composite material is not seriously impaired, especially thefire-barrier and flame-retardant properties of the composite material.

It is known that thin sheets or papers can be formed from suspensions oflamellae of vermiculite, and that such sheets can be used to facecombustible organic foam materials for fire-protection, such a productbeing described for example in our United Kingdom Patent SpecificationNo. 2,007,153. We have observed, however, that when exposed to a firesuch sheets or papers tend to curl and crack and thus do notsatisfactorily retard burning of the substrate do not provide anadequate fire-barrier to protect combustible substrates on which theyarre used as facing materials. By contrast, and surprisingly, we havefound that when the fibrous composite materials of the invention areexposed to a fire they do not curl or crack even when the coating layerof lamellae is extremely thin. Thus the fibrous composite materials ofthe invention provide better fire-barriers than sheets or paperscomprising lamellae alone.

The fibrous composite materials are made by applying the layer minerallamellae to a suitable fibrous substrate. Usually the lamellae will beapplied from a suspension in a carrier liquid which may be for examplean organic liquid, or water or another aqueous medium. Conveniently thesuspension obtained in the process used for chemical delamination oflayer minerals can be used directly to form the fibrous compositematerial. If desired, however, lamellae in the form of a free-flowingdry powder (as described for example in our European Patent PublicationNo. 0009.311A) may be suspended in any suitable carrier liquid forapplication to the fibrous substrate. The solids content (lamellae) ofthe suspension is not critical may vary over a wide range. Any stablesuspension may be employed. Typically, the solids content of thesuspension will be up to 40% by weight of the suspension but may for theproduction of thin coatings be only a few %, say 2% by weight.Preferably the solids content of the suspension for most applicationswill be from 10% to 20% by weight.

After application of the suspension of the layer mineral to the fibroussubstrate, the carrier liquid is removed, usually by evaporation, toleave the lamellae of the layer mineral deposited, preferably as acoherent layer, on the fibrous substrate. If desired excess carrierliquid may be sweezed from or allowed to drain from the compositematerial prior to heating the composite material to remove residualcarrier liquid. The temperature at which the suspension is applied tothe fibrous substrate can be any temperature up to or even greater thanthe boiling point of the carrier liquid, providing of course that thefibres are stable at such temperatures. We prefer to avoid temperaturesabove the boiling point of the carrier liquid since unless care isexercised a rapid evolution of gas may have an adverse effect upon theproperties of the composite material.

The suspension (or slurry as it may also be termed) can be applied tothe fibrous substrate by any known technique, including brushing(painting), spraying, doctoring, licking, knife-coating, `nip`-coating,roller-coating, dip coating and impregnation or, in the case of loosefibres by co-depositing the fibres and layer minerals. It is a simplematter for the operator to choose a suspension strength and anapplication technique appropriate to applying the desired loading oflamellae onto any particular fibrous substrate.

The application technique employed for applying the lamellae to thefibrous substrate may vary, being different perhaps for coatingindividual fibres, strands and rovings than for coating woven, felted orotherwise unified fibrous materials.

If desired, the suspension of lamellae may be gasified to produce afroth for application to the fibrous substrate so that the layer mineralcontent of the resulting composite material may be present as a cellular(rigid foam) matrix. Conversion of a suspension of vermiculite lamellaeto rigid foams is described, for example, in our United Kingdom PatentSpecification No. 1,585,104.

In the case of coating individual fibres or yarns or strands, a specificembodiment of the invention residues in applying the coating duringproduction of the fibre, yarn or strand. Thus for example, in thespinning of fibres such as glass fibres the "green", freshly-extrudedfibres may be coated immediately with the suspension of lamellae, forexample by spraying the fibres at a suitable point below the spinneretteorifice(s) or by spinning the fibres into a bath of the suspension. Analternative technique for coating fibres immediately after theirextrusion is to dust the "green" fibres whilst they are still stickywith powder comprising the lamellae; however, because of theself-adhesion properties exhibited by the lamellae, especiallyvermiculite lamellae when deposited from aqueous suspension we prefer toapply an aqueous suspension to the fibres rather than dry powder.

Another technique for applying the lamellae to fibres is to employ asuspension of the lamellae as a textile size. Thus, for example, thesuspension may be applied to glass fibres as a size using the techniquesdescribed in United Kingdom Patent Specification No. 2,016,993 and by KL Loewenstein in "The Manufacturing Technology of Continuous GlassFibre" (an Elsevier publication).

Another technique particular to a specific product form arises in thecase where the fibrous substrate of the composite material is a mat offibres produced by a wet-lay or paper-making technique in which thefibres are suspended in a carrier liquid, usually water, and the fibremat is laid down from the suspension. In such a case the suspension offibres may include the lamellae by suspending the fibres in a suspensionof lamellae, by suspending lamellae in a suspension of fibres or bymixing suspensions of fibres and lamellae. In this technique, a smallamount of an organic binder, for example a rubber latex or polymer latexis often included in the suspension to afford handleability to theresulting mat, the organic binder subsequently being removed if desiredby burning (provided, of course, that the fibres will withstand theburning conditions).

After application of the suspension of lamellae to the fibroussubstrate, the wet substrate preferably is squeezed or to remove any air(especially bubbles) which may have become entrained, thereby enhancingthe aesthetic appearance and handle of the composite material andreducing the occurrence of blistering of the coating in a fire.

The fibrous composite materials of the invention exhibit improvedfire-performance and high temperature performance compared with thecorresponding material made of the untreated fibres although theK-factor of the treated fibres will usually be slightly higher than thatof the untreated fibres. Thus fibres which are inherently flammable canbe rendered fire-resistance and fire-retardant. It is a general featureof the invention that the fire-performance and thermal properties of allnon-combustible fibres and fibrous materials are upgraded by theapplication to them of a coating of lamellae of a layer mineral.

As stated hereinbefore, vermiculite is the preferred layer material. Thereason for this preference is that in addition to conferring good fireresistance and thermal performance to the fibrous composite materials,chemically delaminated vermiculite when deposited from aqueoussuspensions exhibits excellent self-adhesion properties. Upon removal ofthe water (or other carrier liquid) from suspensions of lamellae ofchemically delaminated vermiculite, the lamellae mutually adheretogether to form a relatively strong layer of vermiculite, and fibrouscomposite materials containing vermiculite lamellae benefit from thisself-adhesion characteristic of the applied lamellae in that thestrength and durability of the composite is enhanced. The depositedvermiculite lamellae may act as an adhesive to bond the fibres of thefibrous substrate together and/or to bond the composite to othermaterials for example to form laminates.

In addition to upgrading the fire resistance and high temperatureperformance of the fibres to which the coating layer of lamellae isapplied, the coating may afford the further advantage of conferringvapour-barrier characteristics and particularly water vapour-barriercharacteristics on the fibrous films deposited from suspensions oflamellae, especially vermiculite lamellae, have low vapour transmissioncoefficients, especially low water-vapour transmission coefficients suchthat the fibrous composite materials of the invention can be used asbarrier layers to inhibit the ingress of water vapour into materialssuch as foams (where the ingress of water can impair the insulationvalue of the foam on ageing) or water-degradable materials.

Another advantage afforded by coating combustible fibres with lamellaeis that the fibres may be rendered flame-retardant. However flame maytend to spread over the surface of the composite material and if desiredthere may be incorporated in the composite material and especially thesurface thereof flame-retardant additives such as halogenated compounds,antimony trioxide aluminium trihydrate, borates and phosphates.

The fibrous composite materials described hereinbefore and comprisingunmodified coatings comprising lamellae of a layer mineral are usefulmaterials for a wide variety of applications. However, in applicationswhere the composite material is liable to be subjected to liquid water,it is preferred to modify the coatings to confer improvedwater-stability upon the composite. Unmodified coatings tend todisintegrate in liquid water; however, they are readily modified to makethem stable in liquid water. Composite materials comprising vermiculitelamellae can be made water stable by treatment with a solution, forexample a saturated solution, of a magnesium salt such as magnesiumchloride, by treatment with ammonia or the vapour of an alkylamine, orby incorporating a water-stability improver in the suspension oflamellae applied to the fibrous substrate, as is described, for example,in our European Patent Publication No. 0.009.310 Al. Suitablewater-stability improvers are particulate compounds sparingly soluble inwater and having a basic reaction in water, for example calcium oxideand magnesium oxide.

Magnesium oxide is the preferred water-stability improver and inaddition to conferring water-stability to the composite material, thisadditive enhances the strength of the composite. Magnesium oxide is aparticularly desirable additive to gasified (frothed) vermiculitesuspensions used to form the composite material in that it additionallyenhances the compressive additive to gasified (frothed) vermiculitesuspensions used to form the composite material in that it additionallyenhances the compressive strength of the cellular (rigid foam)vermiculite matrix of the composite material. The amount ofwater-stability improver will usually be up to 15% by weight, typically10%, by weight based on the lamellae.

Water-proofing of the composite materials, as opposed to improving theirstability in liquid water, can be effected by incorporating a siliconepolymer precursor in the suspension of lamellae prior to application ofthe suspension to the fibrous material, and treating the compositematerial with an acidic gas in the presence of water to polymerize theprecursor and form a silicone polymer in the composite material. Such awater-proofing process is described in our co-pending United KingdomPatent Application No. 8103459. Thus, for example, sodium methylsiliconate can be incorporated in the suspension and the resultingcomposite material treated with carbon dioxide in the presence of water(during drying of the composite material or subsequent to drying thecomposite and re-wetting it). The amount of silicone polymer precursoradded to the suspension will usually be up to about 5% by weight,typically about 2% by weight, based on the lamellae.

Any suspension of lamellae of layer minerals may be used to form thecomposite materials of the invention. Chemical delamination of layerminerals is well known and any of the known chemical delaminationprocesses may be employed, including the processes described forchemically delaminating vermiculite in United Kingdom PatentSpecifications Nos. 1,016,385; 1,076,786; 1,119,305 and 1,585,104 and byBaumeister and Hahn in "Micron" 7 247 (1976). After production, thesuspension of chemically delaminated layer mineral is subjected to awet-classification treatment in which larger particles of the mineralare removed, as is described in respect of suspensions of vermiculitelamellae in U.K. Patent Specification No. 1,593,382. For use in theprocess of the present invention, the suspension is wet-classified to aparticle size (platelets) below 50 microns, so that the suspensionexhibits colloidal properties. Typical suspensions of vermiculitelamellae obtained by the process described in United Kingdom PatentSpecification No. 1,585,104, wet-classified to particles of below 50microns comprise about 40% of particles in the size range 0.4 to 5.0microns. The fibrous composite materials of the invention can be used inany applications where the corresponding fibrous materials are commonlyemployed, and additionally they enable particular fibres to be used innumerous applications where hitherto those fibres have been consideredunusable because they exhibit unsatisfactory fire performance. Thermalinsulation and fire-barrier uses hitherto considered the sole provinceof asbestos, ceramic fibres and refractory fibres are made available toless expensive, less specialist fibres.

Included amongst the many uses of the fibrous composite material of theinvention is the fire-protection of flammable and/or low-meltingmaterials such as rubber and plastic foams, sheets and films, aluminium,wood, paper, cardboard, glass, and the like. For such uses, the fibrouscomposite material may be provided as a loose covering not bonded to theflammable substrate but we have found that best results are obtained ifthe composite is bonded to and laminated with the substrate. Thecomposite may be laminated with the substrate using conventionaladhesive although in most cases where the layer mineral is vermiculite,the adhesive nature of the lamellae deposited from suspension enablesanother adhesive to be dispensed with. Thus for example application ofthe wet composite (i.e. the fibrous substrate plus vermiculitesuspension) will often result in a satisfactory bonding of the compositeto the substrate. Alternatively, the composite may be formed in situ onthe substrate to be protected, for example by coating the substrate withvermiculite suspension and then pressing a fibrous material onto (andinto) the wet vermiculite layer; if desired a further layer ofvermiculite may then be applied over the fibrous material to `face` thelaminate with vermiculite lamellae.

The composite material may if desired contain other substances, e.gsizes, lubricants and binders on the fibres, or conventional fireretardant additives. The fibrous composite materials are also useful inapplications which do not specifically require fire-retardance and goodthermal properties, for example as reinforcement layers for organic andinorganic materials, e.g. polymers, rubbers, plastics and cements. Usesinvolving reinforcement of organic materials with fibres include GRP(glass reinforced plastic) applications.

The invention is illustrated but in no way limited by the followingExamples in which the following general procedure was used to preparethe vermiculite suspensions.

PREPARATION OF VERMICULITE SUSPENSIONS

150 parts of vermiculite ore (Mandoval micron grade, ex-South Africa)are agitated with saturated sodium chloride solution in 1:2 ratio byweight in a tank for 30 minutes at 80° C. This suspension is thencentrifuged and washed with deionised water. The wet cake is transferredto a second tank where the vermiculite is stirred with 1.5N n-butylaminehydrochloride (2:1 liquid:solid ratio) for 30 minutes at 80° C. Thissuspension is then centrifuged and washed with deionised water beforetransferring the wet cake to a swelling tank in which the vermiculite isstirred in deionised water. After swelling, the suspension containsapproximately 20% solids and the particles are random sized in the range300-400 micron. This suspension is then passed through a stone-type millwhich reduces approximately 50% of the particles to platelets of sizeless than 50 microns. This milled suspension is classified in aweir-type centrifugal classifier and the lighter particles with sievesize less than 50 micron are collected for use. Analysis of this 18-21 %solids suspension by photosedimentometer and disc centrifuge revealsthat approximately 40% of the particles have a size ("equivalentspherical diameter") of 0.4-1.0 micron. The solids content of thesuspension is readily adjusted by adding water to it or removing waterfrom it.

EXAMPLE 1

A 4% by weight vermiculite lamellae slurry was prepared using thegeneral procedure described above. Woven cotton sheet of weight 132g/m². was dipped into this slurry and on removal, excess slurry wassqueezed out of the mat. The mat was then dried in air overnight and theweight of vermiculite impregnated in the mat was determined to be 30g/m².

A 200 mm×130 mm sample of the untreated cotton sheet was subjected to afire test over a calor gas burner fitted with a circular jet of diameter40 mm, the sample being held on a tripod stand 30 mm above the burnerjet. The temperature of the flame at the sample position was determinedas 1075° C. The untreated sheet burned through in 28 seconds leaving apowdery residue with little strength.

A sample of the vermiculite-treated cotton sheet was subjected to thefirst test. This sample exhibited surface spread of flame at 4 seconds,but retained its dimensional stability in the flame. The spreading flameextinguished rapidly and the residual cotton char resisted flamepenetration for 80 seconds whereupon a small breakthrough of flameinitiated localised tearing of the structure.

EXAMPLE 2

A variety of textile yarns were treated with vermiculite by dip-coatingin 10% w/w vermiculite slurry and tested at 1075° C. in the gas-flamewith the following results:

    ______________________________________                                                     Vermic-                                                                       ulite on                                                                             Burn through time                                               Yarn        treated   Untreated                                                                             Vermiculite                               Fibre description yarn      Yarn    treated yarn                              ______________________________________                                        Nylon Staple yarn 39.0      1.5  secs 20-30 secs                              6:6   2 × 18                                                            Cotton                                                                              Egyptian    23.9      34   secs 3-5   mins                                    Grey, 2 × 30                                                      Rayon Acetate     15.5      1.8  secs 2-5   mins                                    rayon 2 × 100                                                     ______________________________________                                    

EXAMPLE 3

Samples of Kraft paper (200 mm×150 mm) were prepared in a hand-mouldafter blending unbleached Kraft pump in water with 18% w/w classifiedvermiculite slurry. This technique allows excellent distribution ofvermiculite particles throughout the paper. The samples of paper wereexamined in the 1075° C. gas-flame test with the following results:

    ______________________________________                                                Weight of 15%                                                         Weight of                                                                             vermiculite Weight of dry                                             Kraft pulp                                                                            slurry      paper                                                     (Gm)    (Gm)        (Gm)       Burn through time                              ______________________________________                                        10.9    --          2.40       3    seconds                                   10.9    14          2.90       2    minutes (edge                                                                 cracking)                                 10.9    28          2.90       2    minutes (edge                                                                 cracking)                                 10.9    40          4.59       5    minutes                                   ______________________________________                                    

EXAMPLE 4

A melded polyester fabric of weight 50 g/m² was coated with a 19% byweight suspension of vermiculite lamellae by a knife on roll coatingtechnique to provide a loading of vermiculite of 63 g/m² /(dry weight)on the fabric. The coated fabric was dried in air overnight.

The coated material was flexible and showed no sign of cracking orflaking on repeated flexing. The sample was placed in a bunsen burnerflame and flaring was observed as the polyester burned. However, thesample remained intact in the flame and the residue char retained itsintegrity for 5 minutes, after which time it was removed from the flame.

For purposes of comparison a sample of the untreated polyester fabricwas placed in a bunsen burner flame.This sample ignited instantaneouslyand was completely destroyed in a few seconds.

EXAMPLE 5

An acrylic-bonded polyester non-woven tissue of weight 17 g/m² wascoated with a 19% by weight suspension of vermiculite lamellae anddried. The density of the dry, coated tissue was 94 g/m². The coatedtissue was reasonably flexible. On exposure of the sample to a bunsenburner flame, bried flaming was observed as the polyester burned in theregion contacted by the flame, leaving a residual char which remainedstable in the flame for several minutes before the sample was removedfrom the flame.

We claim:
 1. A combustible fiber coated with lamellae of chemicallydelaminated vermiculite, the lamellae having a thickness of less than0.5 micron and an aspect ratio of at least
 10. 2. A combustible fiber asclaimed in claim 1 wherein the amount of the vermiculite lamellae is atleast 20% by weight of the fiber.
 3. A combustible fiber as claimed inclaim 1 wherein the fiber is a cellulosic fiber.
 4. A combustible fiberas claimed in claim 1 wherein the vermiculite lamellae are substantiallyall of maximum dimension below 50 microns.
 5. A combustible fiber asclaimed in claim 1 wherein said coating additionally comprises awater-stability improver.
 6. A fibrous material comprising an assemblyof individual combustible fibers each fiber having thereon a coating oflamellae of chemically delaminated vermiculite having a thickness ofless than 0.5 micron and an aspect ratio of at least 10.